Process for observing overlay errors on lithographic masks

Abstract

A method of observing overlay errors associated with two masks or reticles includes providing alignment marks to a substrate. The alignment marks can be observed to determine overlay errors. In one embodiment, the lightness or darkness of the alignment marks can indicate an overlay error. The technique can be utilized in any photolithographic system including an EUV, VUV, DUV or conventional patterning device.

What is claimed is:  
     
       1. A method of observing alignment errors between a first mask or reticle and a reticle and a second mask or reticle for fabricating an integrated circuit, the method comprising steps of: 
       providing a photoresist layer over a semiconductor substrate;  
       providing a first pattern of radiation to an area of the photoresist layer with the first mask or reticle, the first pattern of radiation including a plurality of second alignment marks;  
       providing a second pattern of radiation to the area of the photoresist layer with the second mask or reticle, the second pattern of radiation including a plurality of second alignment marks;  
       developing the photoresist layer to reveal a plurality of wafer alignment marks, the wafer alignment marks being related to a combination of the first alignment marks and the second alignment marks; and  
       observing the darkness of the wafer alignment marks.  
     
     
       2. The method of  claim 1 , wherein the first alignment marks and the second alignment marks have an identical pattern. 
     
     
       3. The method of  claim 2 , wherein the identical pattern includes horizontal and vertical bars. 
     
     
       4. The method of  claim 3 , wherein the horizontal bars are 200 nm wide and spaced apart by 400 nm or less. 
     
     
       5. The method of  claim 3 , wherein the vertical bars are located below the horizontal bars. 
     
     
       6. The method of  claim 1 , wherein the first alignment marks are disposed at corners of the first mask or reticle. 
     
     
       7. The method of  claim 1 , wherein the darkness is related to a moire effect. 
     
     
       8. The method of  claim 1 , wherein the observing step includes observing a difference in darkness between the wafer alignment marks. 
     
     
       9. The method of  claim 1 , wherein the first mask or reticle is an EUV mask or reticle. 
     
     
       10. A method of determining an overlay error between a pair of masks or reticles used to fabricate an integrated circuit, the method comprising: 
       providing a pattern of radiation to an area above a substrate with a first mask or reticle;  
       providing a pattern of radiation to the area above the substrate with a second mask or reticle; and  
       providing a plurality of alignment features on the substrate, the alignment features being related to the first mask or reticle and the second mask or reticle, wherein a characteristic of the alignment features can be observed via the naked eye to determine the overlay error between the first mask or reticle and the second mask or reticle.  
     
     
       11. The method of  claim 10 , wherein the characteristic is related to a color or darkness of the alignment features. 
     
     
       12. The method of  claim 10 , wherein the alignment features are provided on corners of the substrate. 
     
     
       13. The method of  claim 12 , wherein the alignment features include vertical and horizontal bars. 
     
     
       14. The method of  claim 13 , wherein the alignment features each include at least ten horizontal bars and at least ten vertical bars. 
     
     
       15. The method of  claim 14 , wherein the horizontal bars are 200 nm wide and the vertical bars are 200 nm wide. 
     
     
       16. A method of determining an overlay error with the naked eye between a first mask or reticle and a second mask or reticle utilized to fabricate an integrated circuit, the method comprising: 
       forming a set of alignment marks on a substrate, the alignment marks being related to alignment patterns associated with the first mask or reticle and the second mask or reticle provided to an area of the substrate, the set of alignment marks having a darkness characteristic related to the overlay error; and  
       observing the darkness characteristic of the alignment marks with the naked eye.  
     
     
       17. The method of  claim 16 , wherein the alignment marks are provided on a peripheral area of the substrate. 
     
     
       18. The method of  claim 16 , wherein the alignment marks are relatively light when the overlay error is small. 
     
     
       19. The method of  claim 16 , wherein the alignment marks include a plurality of vertical and horizontal bars. 
     
     
       20. The method of  claim 19 , wherein the horizontal bars are 200 nm wide and spaced apart by 400 nm.